Inclusion of persistence in the DairyNZ Forage Value Index

Abstract

Inclusion of a persistence trait into the DairyNZ Forage Value Index (FVI) is an important step toward developing a holistic assessment of the relative value to dairy farm businesses of perennial ryegrass (Lolium perenne) cultivars. For the purposes of the FVI, ‘persistence’ was defined as the persistence over time of yield differences between diploid and tetraploid functional groups, and implemented (as an interim step) via two measures: a mean persistence scaling factor (μPS) and a relative pasture renewal cost (RRC). The values of μPS and RRC were estimated by analysing four long-term dry matter (DM) production data sets from across New Zealand, then applied to all cultivars in the 2019 FVI lists. Incorporating persistence reduced the difference in overall FVI value between tetraploids and diploids between $117 and $202/ha (depending on diploid heading date, and region), partially re-balancing the sharp rise in tetraploid values and rankings resulting from incorporation of the metabolisable energy (ME) content trait. Implementing persistence in the FVI at the ploidy level is the first step toward inclusion of cultivar-specific persistence information. This next step will require persistence data for cultivars, plus more information on processes and criteria used by farmers when they decide to renew pastures.